| Strange A/C problem [message #144127] |
Thu, 22 September 2011 12:49  |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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I'm have a strange problem with my A/C. Sometimes it will suddenly stop blowing cold even though the compressor is engaged. It's not an icing problem because sometimes it will start out only blowing warm air. Other times it will blow cold for a period of time then stop...or not.
It's 78 Eleganza II and I've just replaced the compressor and charged the system with DuraCool. System was working fine when last used but had leaked down through compressor seal several years ago and although the engine and generator has been run periodically, not so with the A/C. System was 134A before the compressor swap and was evacuated overnight and let sit for hours with no leaks after the swap.
Low and high side pressures are fine when running but haven't caught it blowing warm with the gauges in place but will keep trying. Is there any kind of vacuum control on the compressor?
1978 Eleganza II
[Updated on: Thu, 22 September 2011 13:58] Report message to a moderator |
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| Re: [GMCnet] Sticky expansion valve? [message #144138 is a reply to message #144136] |
Thu, 22 September 2011 14:25  |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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Compressor engages fine, no issue there. Although, thinking about it now makes me wonder if I have quiet belt slippage. I'm running out of ideas given the circumstances.
1978 Eleganza II
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| Re: [GMCnet] Sticky expansion valve? [message #144151 is a reply to message #144138] |
Thu, 22 September 2011 17:33 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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Put the gauges back on and they read exactly the same as when the system is off. There's a vacuum (10 in) on the low side and about 130 psi on the high side. When running and blowing cold it's 23 psi on the low side and 152 on the high side.
I need to travel across the state Saturday and hope to have this fixed before then.
1978 Eleganza II
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| Re: Strange A/C problem [message #144164 is a reply to message #144127] |
Thu, 22 September 2011 19:21 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Not following... can you restate:
1) pressure readings when running and working correctly
2) pressure readings when running and blowing warm
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Sticky expansion valve? [message #144167 is a reply to message #144151] |
Thu, 22 September 2011 19:32 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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| kwharland wrote on Thu, 22 September 2011 15:33 |
Put the gages back on and they read exactly the same as when the system is off. There's a vacuum (10 in) on the low side and about 130 psi on the high side. When running and blowing cold it's 23 psi on the low side and 152 on the high side.
I need to travel across the state Saturday and hope to have this fixed before then.
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Maybe I am not reading this right. If the system is off you can't have 10" suction and 130 hi side the pressures would be equal after a very short time. If the compressor is running and you have these pressures it would indicate a low charge,iced coil, bad expansion valve or a plugged dryer.If you sometimes have 23 lbs suction and sometimes have 10" ditto.Assuming you had 23 lbs on a hot day I suggest that you add more refrigerant to get the suction a couple of pounds below 30 and see what happens. Did you check the accuracy of your suction gage as Jim suggested?
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Strange A/C problem [message #144168 is a reply to message #144164] |
Thu, 22 September 2011 19:32 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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John:
Compressor running and blowing cold - 23 psi low side, 152 psi high side
Compressor running and blowing hot - 10" vac low side, 133 psi high side.
James:
Pressures indicate it's not a hot water or air mixing problem. I first thought it might be a sticky expansion valve until I figured out this system uses an orifice tube, not expansion value.
1978 Eleganza II
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| Re: Strange A/C problem [message #144169 is a reply to message #144168] |
Thu, 22 September 2011 19:38 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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| kwharland wrote on Thu, 22 September 2011 17:32 |
John:
Compressor running and blowing cold - 23 psi low side, 152 psi high side
Compressor running and blowing hot - 10" vac low side, 133 psi high side.
James:
Pressures indicate it's not a hot water or air mixing problem. I first thought it might be a sticky expansion valve until I figured out this system uses an orifice tube, not expansion value.
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The GMC does not have an orfice tube it is definitely an expansion valve unless some one messed with it. If they did I suggest you put an expansion valve back in it.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Strange A/C problem [message #144170 is a reply to message #144168] |
Thu, 22 September 2011 19:43 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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An easy way to check for a plugged dryer would be to feel the temperature of the pipe going into the dryer if it is more then a few degrees warmer then the pipe leaving the dryer it is restricted but I doubt this is your problem.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Strange A/C problem [message #144188 is a reply to message #144170] |
Thu, 22 September 2011 21:06 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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| roy1 wrote on Thu, 22 September 2011 20:43 |
An easy way to check for a plugged dryer would be to feel the temperature of the pipe going into the dryer if it is more then a few degrees warmer then the pipe leaving the dryer it is restricted but I doubt this is your problem.
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Thanks Roy, I'll try that.
| roy1 wrote |
The GMC does not have an orifiice tube it is definitely an expansion valve unless some one messed with it. If they did I suggest you put an expansion valve back in it.
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That's interesting. One wasn't obvious to me and someone else said it was more likely to be controlled with an orifice tube...but it's older than most people realize, or remember.
Given what else you've said, my guess is the valve is sticking. A clogged dryer would be a consistent blockage. And it fits what I see on the gauges as well. As for accuracy of the gauge, I don't think Jim was suggesting I check it, just that it would explain a 2-3 psi difference. But I don't know why it is assumed that a reading of 23 is incorrect either. Three full cans of Duracool might be slightly too much.
Anyway, I need to find and verify this system has an expansion valve. Anyone got a pic showing it's location? I imagine it's not common for this to be removed during a changeover to 134A.
1978 Eleganza II
[Updated on: Thu, 22 September 2011 21:07] Report message to a moderator |
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| Re: Strange A/C problem [message #144189 is a reply to message #144188] |
Thu, 22 September 2011 21:13 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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http://www.bdub.net/manuals/X7725/X7725.pdf
section 1B-13
| kwharland wrote on Thu, 22 September 2011 22:06 |
| roy1 wrote on Thu, 22 September 2011 20:43 |
An easy way to check for a plugged dryer would be to feel the temperature of the pipe going into the dryer if it is more then a few degrees warmer then the pipe leaving the dryer it is restricted but I doubt this is your problem.
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Thanks Roy, I'll try that.
| roy1 wrote |
The GMC does not have an orifiice tube it is definitely an expansion valve unless some one messed with it. If they did I suggest you put an expansion valve back in it.
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That's interesting. One wasn't obvious to me and someone else said it was more likely to be controlled with an orifice tube...but it's older than most people realize, or remember.
Given what else you've said, my guess is the valve is sticking. A clogged dryer would be a consistent blockage. And it fits what I see on the gauges as well. As for accuracy of the gauge, I don't think Jim was suggesting I check it, just that it would explain a 2-3 psi difference. But I don't know why it is assumed that a reading of 23 is incorrect either. Three full cans of Duracool might be slightly too much.
Anyway, I need to find and verify this system has an expansion valve. Anyone got a pic showing it's location? I imagine it's not common for this to be removed during a changeover to 134A.
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C. Boyd
76 Crestmont
East Tennessee
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| Re: Strange A/C problem [message #144209 is a reply to message #144189] |
Thu, 22 September 2011 22:40 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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That's what I needed! Now I know why I didn't see the expansion valve at a glance...it's hidden inside the evaporator box! Thanks!
1978 Eleganza II
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| Re: Strange A/C problem [message #144228 is a reply to message #144226] |
Fri, 23 September 2011 08:44 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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Thanks for the reply Matt. I do believe the symptoms point to an expansion valve problem, but not from icing as it will as often as not start up blowing warm air.
The system was only open for several minutes, just long enough to swap the header from one compressor to the other. It was put under full (~30") vacuum for 12 hours, then let sit for another 4 hours to leak testing.
An A/C engineer I've spoken to talks about a waxy substance that can build up in the expansion valve and says in some cases warming the valve will free it up. I'm off to try that shortly, certainly no harm in trying.
1978 Eleganza II
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| Re: Strange A/C problem [message #144268 is a reply to message #144228] |
Fri, 23 September 2011 11:53 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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| kwharland wrote on Fri, 23 September 2011 06:44 |
Thanks for the reply Matt. I do believe the symptoms point to an expansion valve problem, but not from icing as it will as often as not start up blowing warm air.
The system was only open for several minutes, just long enough to swap the header from one compressor to the other. It was put under full (~30") vacuum for 12 hours, then let sit for another 4 hours to leak testing.
An A/C engineer I've spoken to talks about a waxy substance that can build up in the expansion valve and says in some cases warming the valve will free it up. I'm off to try that shortly, certainly no harm in trying.
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When it comes to removing air from the system it is always a good practice too pull a short vacuum break it with refrigerant (ANY kind) then pull your deep vacuum. Very often I do this twice. If there is air in the system it generaly shows up as excessive discharge pressure as it is a non condensible. Don't forget an iced up txv is most often caused by low suction pressure from being a little short on the refrigerant charge.
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Strange A/C problem [message #145886 is a reply to message #144268] |
Fri, 07 October 2011 22:41 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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I've finally got back on the A/C project. I was going to warm the expansion valve while the unit was running but unfortunately I left the gauges on overnight and the coolant leaked out. So I bit the bullet and got a new expansion valve and dryer.
Unfortunately the new valve doesn't look like the old one. The one in place has two small tubes but the new one only has one. What to do?
1978 Eleganza II
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